نشریه دفاع هوافضایی
سال دوم شماره 2 (پیاپی 6، تابستان 1402)

The spectrum of electromagnetic waves in ku band has a great impact on equipment and manpower. Many methods have been used to protect electronic equipment against this range of waves. In this paper, uniform and non-uniform cold plasma consisting of three rectangular layers is used. Each plasma layer has different parameters such as thickness, impact frequency, magnetic property, variable density and wavelength of radiation. The electromagnetic input wave with p polarization is considered at different angles in the ku band. By solving the wave equations and calculating the acceptance coefficient in single and triple plasma layers, the optimal value of total absorption and reflection is calculated. Then, using Mathematica software, the diagrams are drawn according to the parameters mentioned in the single-layer blade and the three-layer blade. Using these diagrams, the cop protection coefficient in single-layer and three-layer states is compared by considering consecutive reflections in magnetic and non-magnetic cases, and the desired results are presented. The results show that using three-layer plasma leads the cop coefficient to its optimum for high bandwidth.

In this article, a rectana microstrip antenna with optimal dimensions in the GSM band is proposed to harvest Rf energy and convert it into electricity. The proposed antenna is a special model of bow-tie antenna whose triangles are placed at 90 degrees to each other and it is fed in dipole form with SMA connector. The dimensions of the antenna are 10 x 10 cm with an FR4 substrate with a thickness of 1.6 mm, which is designed to receive in the GSM frequency band, i.e. 900 and 1800 MHz. The recommended antenna gain is 1.8dBi. The advantage of the proposed antenna compared to the examined antennas is the high efficiency of the RF to DC converter circuit and its small size. So that the efficiency factor obtained for it is 76%, which is 12% more than the previous examples. Also, the volume occupied by the proposed structure is at least 87.2% less than the structures presented in other references for this frequency band. On the other hand, due to the flatness of the proposed structure, this antenna has the ability to be used on flat surfaces such as the wall or body of various objects, while the antennas proposed in other references are 3D and lack this capability.

The main design goal of thermal control subsystem is to keep the temperature of the satellite equipment within specified margins. Satellite experienced extreme hot and cold conditions during the mission, so it is difficult to choose the materials and surface coatings for these conditions. If design is done to deal with hot conditions, satellite power for keeping warm in cold conditions is increased and this is while supply of required power for heating the satellite in cold conditions is one of the important design concerns. Due to restrictions in space systems for power supply, the value of power for thermal control subsystem should be optimal. This paper describes the process of designing a thermal control subsystem of small satellites using a simple model. In the present study, the thermal design is done by using the optimal choice for the radiator cover. This design has been done in a way that the least amount of heater power is required. For this purpose, optimization and linear programming have been used. Simulation results show that satellite temperature in warm and cold conditions is in the range and this method significantly reduces the amount of required power heater.

In this study, the numerical investigation is carried out for fin heat transfer used in internal combustion engines in drones, cars, and motorcycles, while the geometry, configuration, cooling flow regime, and priority of using each of them was studied at different conditions. Also, introduction of geometry, boundary condition and meshing was done by GAMBIT and the numerical solution was done by FLUENT while the K-ω was preferred turbulent model. It found that the heat transfer of singular and group fins was dependent on the flow behavior on the surface and its penetration respectively. Also, the average heat transfer coefficient in convex parabolic fin against the laminar and turbulent flow was 336 and 45.24 percent more than rectangular and 82.8 and 9.4 percent more than triangular, respectively, while its volume was less than 88.77 and 77.55 percent in comparison with rectangular and triangular respectively. So this fin can be considered in the cooling of light equipment engines. Also, the results of material effects on parabolic fin heat transfer showed a change of conductivity could be effective only for tall fins.

In the last few decades, a lot of research has been done based on various analytical methods in the measurement of amino acids in environmental and biological samples such as blood serum due to their important role in the functioning of the body's vital organs and also its indirect effect on the defense power. The use of colorimetric chemical sensors has attracted the attention of many researchers due to the simplicity of the method, good selectivity, cheapness, low equipment, no need for pre-preparation of the sample, usable for all samples, especially biological samples and detection with the naked eye. In this research, the colorimetric method based on ArsenazoIII (2,7-bis[(2-arsonophenyl) azo]-1,8-dihydroxy-3,6-naphthalenedisulfonic acid) (AAIII) (as a colorimetric chemical sensor) was used to determine arginine in aqueous medium. The addition of arginine to AAIII solution caused a visible color change from red to purple and a decrease in absorption at 536 nm wavelength. An isosbestic point was observed at 580 nm, which indicates the interaction between AAIII and arginine. The linear dynamic range for the UV-Vis absorption test was 15-340 μmolL-1. The detection limit was calculated to be 0.04 μmolL-1. This method was used to determine arginine in environmental, which had satisfactory resuls.

The Ni doped CdSe nanostructured thin films during deposition procedure that govern altering of the optical transitions have been investigated. Concentration of Ni as doping inside CdSe from 0.03 mol in form of nanostructured thin layers have been fabricated through a simple chemical solution deposition approach. Doping of the Ni to CdSe add the new transitions in related to NiSe, means the tiny concentration of Ni ions create the new transition to CdSe that sample have multiple optical bandgap. Although absorption due to impurity can be considered as absorption inside band gap region below the fundamental (band-to-band) but absorption due to doping in nanostructured thin films aren’t as absorption inside band gap and their optical transitions are band to band so have broad lines and powerful in absorption spectra. There is an order in band gap changing with doping concentration raising so that increasing of the Ni2+ions decreases the optical band gap to 1.59eV although optical band gap for CdSe in bulk state is 1.74eV , so doping procedure decreases optical bandgap of CdSe that is mean doping procedure creates the new structure. It has shown that it’s possible to determine the Urbach energy of the samples from the absorption spectrum without the need to determine the adsorption coefficient from the determination of thickness.